Polybrominated diphenyl ethers (PBDEs) are an important class of flame retardants. Because of their presence in maternal milk and their structural similarity to polychlorinated biphenyls (PCBs), concern has been raised on their possible developmental neurotoxicity. Aim of the present study was to investigate the in vitro effects of PBDE-99 (2,2', 4,4',5-pentabromodiphenyl ether) on astroglial cells (human 132-1N1 astrocytoma cells) and comparing it with those of the PCB mixture Aroclor 1254. Both PBDE99 and Aroclor 1254 caused a concentration-dependent inhibition of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) reduction, however, only the latter increased lactate dehydrogenase (LDH) release or cell death, assessed by the trypan blue assay. PBDE-99 caused translocation of the three protein kinase C (PKC) isozymes (alpha, epsilon, zeta) present in 132 astrocytoma cells, while Aroclor 1254 affected only PKCalpha and epsilon translocation. However, pre-incubation with the PKC inhibitor GF109203X or PKC down-regulation by the phorbol ester PMA, had minimal or no effect on PBDE-99 or Aroclor 1254-induced cytotoxicity. Similarly, the calcium chelator BAPTA-AM, the tyrosine kinase inhibitor genistein, and the MEK (mitogen activated protein kinase kinase) inhibitor PD98059 had no effect on PBDE-99 and Aroclor 1254 cytoxicity. On the other hand, the phosphatidylinositol 3 kinase (PI-3K) inhibitor LY290042 enhanced PBDE-99 toxicity, but did not affect Aroclor 1254. Because of the involvement of PI-3K in apoptotic cell death, the ability of PBDE-99 and Aroclor 1254 to induce apoptosis in astrocytoma cells was investigated. PBDE-99, but not Aroclor 1254, caused apoptotic cell death in astrocytoma cells, assessed by the TUNEL method and by Hoechst 33258 staining, via a p53 dependent mechanism. These results suggest that PBDE-99 and Aroclor 1254 exert differential cytotoxic effects on human astroglial cells.